Termination device and method

ABSTRACT

A device for terminating a cable having a screen and at least one inner conductor comprises: 
     (i) a hollow electrically conductive outer body for terminating the screen of the cable, which has two open ends and which is provided with an internal screw thread that tapers from one of its open ends; 
     (ii) a metallic coil, at least part of which is screwed into the tapering screw thread of the outer body and tapers towards a constriction at least when screwed into the tapering screw thread; and 
     (iii) a conformable metallic foil in tubular form, at least part of which is located within the constriction of the metallic coil; 
     the device being arranged so that the screen of the cable may be terminated by inserting an exposed portion of it into the tube of metallic foil and screwing the metallic coil further into the outer body by means of the tapering screw thread, thereby constricting the coil further and causing the metallic foil to tighten about the cable screen.

This invention relates to the termination of screened cables, includingcoaxial cables and screened wires.

The need to match the characteristic impedance of a signal transmissioncable with the nominal impedance of the cable's termination is wellknown. Impedance mismatch typically produces reflections of thetransmitted signal, resulting in undesirable signal attenuation and theproduction of echos which transmit false information.

In an effort to produce impedance-matched terminations of signaltransmission cables, a variety of termination methods have been used,the most common of which involve crimping, clamping and/or soldering.For example, U.S. Pat. No. 3,541,495 discloses a connector forterminating a coaxial cable, having an outer contact body forterminating the cable braid. The outer contact body is provided with awindow which is covered by a heat-recoverable sleeve, and locatedbetween the sleeve and the window is a ring of solder. In order toterminate the braid of a coaxial cable inserted into the device, theheat-recoverable sleeve is heated, causing the solder to melt and form aconnection between the braid and the outer contact body. Whilst thistype of connector may be used to form reliable terminations of coaxialcables, it is prone to impedance mismatch, because the internal diameterof the outer contact body of the connector inevitably has to be greaterthan the external diameter of the cable braid, in order to enable easeof insertion of the cable. The characteristic impedance of a coaxialcable is dependant upon the ratio between the diameter of the outerconductor and the diameter of the inner conductor, and so any change inthe position of the outer conductor (e.g. the change from cable screento outer contact body) will alter the characteristic impedance.

A coaxial cable termination device which generally provides a muchgreater degree of impedance matching is manufactured and sold by RaychemCorporation of Menlo Park, Calif., USA and Raychem S. A of CergyPontoise, Paris, France, under the trade mark "PLUGPAK". This deviceutilises a tinned copper braid and a ring of solder located inside aheat recoverable sleeve in order to terminate the braid of a coaxialcable. In use, the sleeve is heated, causing it to shrink about theexposed braid of a coaxial cable inserted into the device, and causingsolder ring to melt. Because its strands are relatively loosely braided,the tinned copper braid of the device is also able to shrink indiameter, and this normally eliminates the possibility of impedancemismatch at the termination, which may have arisen due to a change inthe distance between the inner and outer conductors. However, the degreeto which this shrinkage is possible is limited by the braid itself andthe construction of the device, and it has been found that whenrelatively small diameter cables are terminated using this device,impedance mismatch may sometimes occur. There is therefore a need for atermination device which provides impedance matching whilst being ableto terminate a greater range of cable sizes. More generally, there isalso a continual need to improve upon the methods of terminating alltypes of screened wires and cables, and in particular to increase thereliability of their terminations in terms of screening effectivenessand grounding of the cable screen.

According to one aspect of the present invention, there is provided adevice for terminating a cable having a screen and at least one inner:conductor, which comprises:

(i) a hollow electrically conductive outer body for terminating thescreen of the cable, which has two open ends and which is provided withan internal screw thread that tapers from one of its open ends;

(ii) a metallic coil, at least part of which is screwed into thetapering screw thread of the outer body and tapers towards aconstriction at least when screwed into the tapering screw thread; and

(iii) a conformable metallic foil in tubular form, at least part ofwhich is located within the constriction of the metallic coil;

the device being arranged so that the screen of the cable may beterminated by inserting an exposed portion of it into the tube ofmetallic foil and screwing the metallic coil further into the outer bodyby means of the tapering screw thread, thereby constricting the coilfurther and causing the metallic foil to tighten about the cable screen.

According to another aspect of the invention, there is provided a methodof terminating a cable having a screen and at least one inner conductorby means of a device according to the invention, which comprises:

(i) inserting an exposed length of the cable screen into the tube ofmetallic foil; and

(ii) screwing the metallic coil further into the outer body until themetallic foil has tightened about the exposed length of the cablescreen.

According to a further aspect of the invention, there is provided acable having a screen and at least one inner conductor, which isterminated by means of a device according to the invention. Preferablythe cable is a coaxial cable.

The invention applies generally to cables which have a screen and atleast one inner conductor, including screened multi-conductor cables andscreened wires, but it is particularly applicable to coaxial cables.

The invention has a number of advantages. The device according to theinvention may be used to terminate a range of cable sizes with improvedimpedance matching, because the metallic foil may be tightened about thecable screen of any one of a range of differently sized cables byscrewing the metallic coil further into the outer body. It is possibleto form a termination that is substantially impedance matched becausethe tube of metallic foil when tightened, provides a screen having aninternal diameter which differs from that of the cable screen only bysubstantially the thickness of the cable screen itself. As well asimproved impedance matching, the invention generally provides secure andreliable cable terminations because the metallic foil once tightenedabout the cable screen, forms an electrical connection with the cablescreen that has a relatively low contact resistance, and the foil andthe metallic coil together provide a degree of strain relief againstbending.

The metallic foil may, for example, conform to, and be tightened about,a cable screen by being crushed by the metallic coil. Preferablyhowever, the tube of metallic foil comprises a spiral wrap, wherein oneportion of the foil overlaps another portion. This has an advantage inthat, in use, constricting the coil further normally causes the spiralwrap of foil to tighten about a cable screen inserted into it.Additionally or alternatively, the metallic foil is preferablyresiliently conformable. This has an advantage in that the resilience ofthe foil may be used to hold the foil in place prior to terminating acable, since it may cause it to grip the constriction of the coil or theinside of the outer body.

The metallic foil may be formed from any appropriate metal, metal alloyor combination of metals or metal alloys, but preferably it is formedfrom copper, e.g. spring temper copper. In particular, it is preferredthat the foil is formed from copper that has a layer of tin on at leastone surface, and especially on both surfaces.

As mentioned above, screwing the metallic coil of the device furtherinto the outer body by means of the tapering screw thread constricts thecoil further. In its undeformed state, the metallic coil may have agenerally right cylindrical shape, but it is preferred for it to taperin the same direction as the internal screw thread of the conductiveouter body. This normally makes it easier to screw the coil further intothe outer body, since less deformation of the coil is required. The coilis preferably resiliently deformable. This has an advantage in that if,subsequent to the formation of a termination, the coil is partlyunscrewed from the tapering screw thread of the outer body, it willnormally expand with the screw thread and therefore remain screwed intothe outer body.

The metallic coil is preferably formed from metal wire, and the metalwire may generally have any cross-section which will enable the coil tobe screwed into the conductive outer body. Preferably, however, themetal wire has a ridge extending along its length which provides thecoil with an external screw thread. Most preferably the wire has apolygonal cross-section, and in this case at least one of the angledportions of the cross-section may form the ridge extending along thelength of the wire.

The metallic coil may be formed from any appropriate metal, metal alloyor combination of metal or metal alloys, but preferably it is formedfrom copper, e.g. hard temper copper.

According to a preferred embodiment of the invention, at least part ofboth the metallic coil and the metallic foil are contained within anelectrically insulating sleeve. More preferably, at least part of theelectrically insulating sleeve of the device is dimensionallyheat-recoverable. A dimensionally heat recoverable sleeve is an articlewhich has a dimensional configuration which may be made substantially tochange when subjected to heat treatment. Usually, such articles recover,on heating, towards an original shape from which they have previouslybeen deformed, but the term `heat-recoverable`, as used herein, alsoincludes articles which, on heating, adopt a new configuration, even ifthey have not previously been deformed.

The heat-recoverable sleeve may comprise a heat shrinkable article madefrom a polymeric material exhibiting the property of elastic or plasticmemory as described, for example, in U.S. Pat. Nos. 2,027,962, 3,086,242and 3,597,372. As is made clear in, for example, U.S. Pat. No.2,027,962, the originally dimensionally heat-stable form may be atransient form in a continuous process in which, for example, anextruded tube is expanded, whilst hot, to a dimensionally heat-unstableform but, in other applications, a preformed dimensionally heat-stablearticle is deformed to a dimensionally heat-unstable form in a separatestage.

Preferably the sleeve is attached to part of the metallic coil and isnot attached to the outer body of the device, so that in use the sleevemay be twisted in order to screw the metallic coil further into theouter body and thereby tighten the metallic foil about the screen of thecable inserted into the device. Where the sleeve is dimensionallyheat-recoverable, it may then be heated in order to cause it to recoverabout the coil and preferably also part of both the cable and the outerbody of the device.

The sleeve is preferably formed from a polymeric material. Preferredmaterials include : low, medium or high density polyethylene; ethylenecopolymers, e.g. with alpha olefins such as 1-butene or 1-hexene, orvinyl acetate; polyamides, especially Nylon materials, e.g. Nylon 6,Nylon 6.6, Nylon 11 or Nylon 12; and fluoropolymers, e.g.polytetrafluoroethylene, polyvinylidenefluoride,ethylene-tetrafluoroethylene copolymer or vinylidenefluoridetetrafluoroethylene copolymer.

According to another preferred embodiment of the invention, where theelectrically insulating sleeve is dimensionally heat-recoverable, itcontains a quantity of fusible polymeric material, preferably in theform of a ring, located beyond one end of the metallic coil. Morepreferably, the polymeric material is located such that, in use, whenthe sleeve is recovered the material will fuse between the sleeve andthe outer jacket of a cable inserted into the device. The polymericmaterial so fused may help to seal the cable termination from moistureingress and/or it may provide strain relief to the termination.

The fusible polymeric material according to the invention preferablycomprises a hot-melt adhesive. The material may, for example, be formedfrom an olefin homopolymer or from a copolymer of an olefin with otherolefins or ethylenically unsaturated monomers. Preferred examplesinclude high, medium or low density polyethylene or ethylene copolymerswith alpha olefins, especially C3 to C8 alpha olefins, vinyl acetate orethyl acrylate. Alternatively, the material may be formed frompolyamides, polyesters, halogenated polymers and the like. Preferredpolyamides include those having an average of at least 15 carbon atomsbetween amide linkages, for example those based on dimer acids and/ordimer diamines. Examples of such adhesives are given in U.S. Pat. Nos.4,018,733 to Lopez et al and 4,181,775 to Corke, the disclosures ofwhich are incorporated herein by reference.

According to a further preferred embodiment of the invention a solderpreform is located inside the electrically insulating sleeve, and morepreferably, it is located about the metallic coil. The preform may haveany one of a number of different shapes, but preferably it is eithersubstantially annular or substantially frusto-conical.

In a particularly preferred embodiment of the invention, the solderpreform comprises a length of solder in the form of a strip that hasbeen wrapped into the shape of a ring so that one portion of the stripoverlaps another portion. The formation of a solder ring by wrapping astrip or ribbon of solder about itself spirally has an advantage in thatonly a single solder feedstock is necessary for forming a range ofsolder ring sizes. Another advantage is that where a tapering metalliccoil is used and the solder preform is located about the coil, and inuse the coil is screwed further into the outer body, the solder preformwrap may unwind sufficiently to accommodate the windings of the coilwhich have a greater diameter than the windings about which the preformwas originally located.

The device according to the invention may be heated in order to melt thesolder preform, subsequent to tightening the metallic foil about thescreen of a cable inserted into the device. Where the device includes aheat-recoverable sleeve, heating it may cause both the solder to meltand the sleeve to recover. At least some of the molten solder willnormally flow through gaps between the windings of the metallic coil,and when the sleeve is heat-recoverable, the recovery of the sleeve willnormally force most of the molten solder through these gaps. Therefore,when cooled and solidified, the solder will normally stiffen themetallic coil and strengthen the contact between the coil and the foil.In addition, for embodiments of the invention in which the metallic foilhas a layer of tin on one or both surfaces, heating the device willnormally cause the tin to melt, and when cooled the foil will thereforenormally be bonded in its tightened arrangement about the cable screenand bonded to the screen itself.

The solder preform may be formed from any one or more appropriate soldercompositions. For example, it may be formed from an Sn₆₃ Pb₃₇ eutecticcomposition which will melt as the device is heated. Alternatively, thesolder preform may comprise a composite having a portion that is formedfrom a relatively high melting point solder, as described inInternational Publication No. WO88/09068. In this form of device,melting of the higher melting point component e.g. Sn₉₆.5 Ag₃.5 eutecticwill normally provide a visual indication that the device has beenheated sufficiently to melt the lower melting point component and toform a satisfactory solder joint. If desired, the lower melting pointcomponent may be of non- eutectic composition and, for example asdescribed in International Publication No. WO90/09255, the higher andlower melting point components may together form a eutectic composition.For example, a non-eutectic Sn₆₀ Pb₄₀ lower melting point component maybe employed with a higher melting point component formed from pure tinin relative amounts such that an Sn₆₃ Pb₃₇ eutectic is formed. Thedisclosures of these two patent applications are incorporated herein byreference. An advantage of employing a two component solder, andespecially a tin, Sn₆₀ Pb₄₀ combination is that it reduces thepossibility of `wicking`, that is to say, travel of the solder away fromthe joint area due to capillary action, which can be caused by prolongedheating of the device.

A particularly preferred embodiment of the invention is one whichfurther comprises at least one inner electrical connector that iselectrically insulated from the conductive outer body, for terminatingthe or each inner conductor of a cable. Any appropriate element forterminating the inner conductor(s) may serve as the electricalconnector(s). The inner conductor(s) may, for example, be crimped,clamped, or soldered to the connector(s), but soldering is generally thepreferred method since this normally produces the most robust andreliable type of termination. It is preferred for there to be a singleinner electrical connector in the device. More preferably, this innerelectrical connector comprises the central pin or socket of a coaxialconnector, such as employed, for example, in BNC, TNC and SMA connectorsand the like.

Preferably, the or each inner electrical connector contains at least onesolder insert, for forming a soldered connection with the innerconductor(s). For example, the conductor(s) may have a hollow portionfor receiving the inner conductor(s) of a cable inserted into thedevice, the hollow portion also containing a quantity of solder. Thesolder may be present in any appropriate form, for example as a ring,ball or pellet.

The or each inner electrical connector may advantageously contain atleast one aperture for enabling the operator, in use, to determinewhether or not the solder contained in the connector has been heatedsufficiently for it to melt and form a solder connection with theconductor(s) of a cable. For example, where there is a single innerconnector which comprises the central pin or socket of a coaxialconnector, it may contain one or more apertures arranged transversallyto the pin or socket. When the solder has melted and flowed, theoperator may determine this by perceiving that either the solder hasflowed away from the aperture(s) or that some of the solder has flowedinto the aperture(s).

The or each inner electrical connector may additionally or alternativelycontain resiliently deformable means for accommodating a range of sizesof inner conductor(s). The resiliently deformable means may comprise,for example, at least one strip of metal or at least one metallic coil(sometimes referred to as a `stuffer coil`) which is capable of beingresiliently deformed by the insertion of the inner conductor(s) of acable into the connector(s). The use of resiliently deformable means mayhave a number of advantages: firstly, it may help to retain the innerconnector(s) prior to formation of a soldered connection; secondly, itmay help to retain each solder insert inside the inner electricalconnector(s) prior to melting of the solder; and thirdly, it may aid theflow of molten solder toward the inner conductor(s), by capillary actionor `wicking`, thereby improving the soldered connection.

The or each electrical connector is electrically insulated from theouter body preferably by means of an electrical insulator whichseparates the connector(s) from the outer body. The insulator preferablycomprises a body formed from a relatively rigid polymeric composition,such as for example polytetrafluoroethylene, high-density polyethyleneor polyvinylidene fluoride.

A device according to the invention will now be described by way ofexample with reference to the accompanying drawings in which:

FIG. 1.is a section elevation along the axis of a device according tothe present invention;

FIG. 2 is a sectional elevation along the axis of the device shown inFIG. 1, showing a coaxial cable inserted therein;

FIG. 3 is a sectional elevation along the axis of the device of FIGS. 1and 2, showing a coaxial cable terminated therein; and

FIG. 4 is a graph showing Voltage Standing Wave Ratio (VSWR) againstsignal frequency as calculated for a device according to the inventionand a prior art cable termination.

Referring to FIG. 1 of the accompanying drawings, a device 1 forterminating a coaxial cable comprises a hollow electrically conductiveouter body 2, an inner electrical connector 3, a metallic coil, 4 aspirally wrapped strip of metallic foil 5, a solder preform 6, aheat-recoverable sleeve 7, a solder insert 8, a stuffer coil 9, aninsulating body 10 and a fusible polymeric ring 27.

The conductive outer body 2, which is for terminating the screen of acoaxial cable, is formed from nickel plated brass. The outer body 2 hasan internal screw thread 11 which tapers from an open end 12 of theouter body, and partly screwed into this tapering screw thread is themetallic coil 4. The coil 4 is formed from copper wire of squarecross-section. Located partly inside the metallic coil 4 and partlyinside the outer body 2 is the spirally wrapped strip of metallic foil5. Two overlapping portions of the strip are indicated by 13 and 14. Thefoil 5 is formed from copper of spring temper and is tin plated on bothsurfaces.

Located about the metallic foil 5 is the solder preform 6. The preform 6is substantially frusto-conical and is a composite strip comprising aportion 15 that is formed from Sn₆₃ Pb₃₇ (i.e. having a relatively lowmelting point) and a portion 16 that is formed from Sn₉₆ Ag₄ (i.e.having a relatively high melting point). The composite strip of thesolder preform 6 has been wrapped into the shape of a frusto-conicalring so that one portion of the strip overlaps another portion (thisfeature is not illustrated in the drawings). The solder preform 6,together with the metallic coil 4, part of the outer body 2 and thefusible polymeric ring 27 are contained within the heat-recoverablesleeve 7. The sleeve 7 has been at least partially recovered about thecoil 4 in the region indicated by 17. The sleeve is formed fromcross-linked and expanded polyvinylidene fluoride.

Contained within the outer body 2 is the insulating body 10, which isformed from polytetrafluoroethylene. Located partly within theinsulating body 10 is the inner electrical connector 3, which is forterminating the inner conductor of a coaxial cable, and is formed fromgold plated brass. The connector 3 has a hollow portion 18, into whichthe inner conductor may be inserted, containing the stuffer coil 9 andthe solder insert 8. The stuffer coil 9 is formed from tin-plated copperwire and the solder preform is formed from Sn₆₃ Pb₃₇.

The device shown in FIG. 1 may be attached to the body of one part of acoaxial connector, such as for example a BNC, TNC or SMA connector orthe like. The conductive outer body 2 may, for example, be screwed intothe back shell of the coaxial connector by means of the screw thread 19.The inner electrical connector 3 comprises the central male contact pinof the coaxial connector. In alternative versions of the device, theelectrical connector 3 comprises the central female contact of thecoaxial connector.

Referring now to FIG. 2, the end of a coaxial cable 20 is shown insertedinto the device of FIG. 1. The end of the cable 20 has been prepared bythe cable jacket 21, the cable screen 22 (a braid) and dielectric 23having been cut back so as to expose appropriate lengths of the innerconductor 24, the dielectric and the screen. The end of the cable hasbeen inserted into the device 1 through the open end 25 of the sleeve 7and the ring of fusible polymeric material 27, so that an exposed lengthof the cable screen 22 has also been inserted into the spiral wrap ofmetallic foil 5 and most of the exposed length of the inner conductor 24has been inserted into the hollow portion 18 of the inner connector 3.The metallic coil 4 has then been screwed further into the outer bodyuntil the spiral wrap of metallic foil 5 tightened about the exposedlength of cable screen 22.

FIG. 3 shows the device 1 of FIGS. 1 and 2 with the coaxial cable 20 ofFIG. 2 terminated therein. The device 1 has been heated, subsequent totightening the metallic foil 5 about the cable screen 22 as describedabove. Heating the device 1 has caused the solder preform 6, the solderinsert 8 and the ring of fusible polymeric material 27 to melt and thesleeve 7 to recover about the metallic coil 4, the cable 20 and theouter body 2.

The melting of the solder insert 8 has caused a soldered connection tobe formed between the inner conductor 24 of the coaxial cable 20 and theinner electrical connector 3. The molten solder insert has flowed intothe spaces between the stuffer coil 9, the inner conductor 24 and theinner connector 3 due to capillary action, and in so doing has flowedaway from the aperture 26, thereby allowing the operator to determinewhether or not the device has been heated sufficiently to form thesoldered connection.

The recovery of the sleeve 7 about the coil 4 has forced most of themolten solder of the preform 6 between gaps in the coil and a solderedconnection has therefore been formed between the coil and the metallicfoil 5. The applied heat has also melted the tin which was plated onboth surfaces of the metallic foil 5 and therefore the foil wrap hasbeen bonded in its tightened arrangement about the screen 22 of thecable and has also been bonded to the screen itself. The operator hasbeen able to determine that sufficient heat has been applied to thedevice 1 in order for these processes to take place by observing thedisappearance of the profile of the solder preform 6 under the recoveredsleeve 7. In particular, the disappearance of the profile of therelatively high melting point portion 16 of the composite solder preformhas indicated that the lower melting point solder portion 15 has fullymelted and flowed.

The recovery of the sleeve 7 about the jacket 21 of the cable 20 hascaused the molten polymeric material 27 to fuse between the cable jacketand the sleeve. This has provided additional strain relief to thetermination and has sealed the termination against moisture ingress.

Referring now to FIG. 4, this shows graphs of calculated (i.e.estimated) Voltage Standing Wave Ratio (VSWR) against Signal Frequencyfor two sizes of coaxial cable (RG316 and RG178) and for a deviceaccording to the invention and a PLUGPAK (trademark) termination device(as mentioned above). Each of graphs 1 to 4 represents the variation incalculated VSWR with signal frequency for the devices and cables asfollows:

Graph 1. A device according to the invention installed on RG316 cable.

Graph 2. A PLUGPAK device installed on RG316 cable.

Graph 3. The device of graph 1 installed on RG178 cable.

Graph 4. The device of graph 2 installed on RG178 cable.

The graphs show that for each size of cable, the device according to theinvention exhibits smaller calculated VSWR than the PLUGPAK device overthe signal frequency shown. It also shows that for smaller diametercables (e.g. RG178 as shown) the device according to the inventionexhibits a significant reduction in calculated VSWR compared to thePLUGPAK device. This is an illustration of the improved ability of thedevice according to the invention substantially to provide impedancematching for a range of cable sizes.

For example, at a signal frequency of 4 GHz, the calculated VSWR of eachdevice for a given cable size is:

Graph 1 (Device according to the invention on RG316): 1.01

Graph 2 (PLUGPAK device on RG316): 1.02

Graph 3 (Device according to the invention on RG178): 1.11

Graph 4 (PLUGPAK device on RG178): 1.66

The graphs and values of VSWR were calculated on computer from a modelof the electrical performance (in terms of VSWR) of the termination ofthe screen (only) of each coaxial cable by the respective terminationdevice.

In the calculations of VSWR, the following mathematical formulae wereused: ##EQU1## where R is the complex reflection, defined as: ##EQU2##where Z is the estimated impedance of the device at the cable screentermination and Zo is the characteristic impedance of the cable.

I claim:
 1. A device for terminating a cable having a screen and atleast one inner conductor, which comprises:(i) a hollow electricallyconductive outer body for terminating the screen of the cable, whichbody has two open ends and which is provided with an internal screwthread that tapers from one of its open ends; (ii) a metallic coil, atleast part of which is screwed into the tapering screw thread of theouter body and tapers towards a constriction at least when screwed intothe tapering screw thread; and (iii) a conformable metallic foil intubular form, at least part of which is located within the constrictionof the metallic coil;the device being arranged so that the screen of thecable may be terminated by inserting an exposed portion of it into thetube of metallic foil and screwing the metallic coil further into theouter body by means of the tapering screw thread, thereby constrictingthe coil further and causing the metallic foil to tighten about thecable screen.
 2. A device as claimed in claim 1, wherein the metalliccoil tapers in the same direction as the internal screw thread of theconductive outer body.
 3. A device as claimed in claim 1, wherein themetallic coil is resiliently deformable.
 4. A device as claimed in claim1, wherein the metallic coil is formed from metal wire which has a ridgeextending along its length which provides the coil with an externalscrew thread.
 5. A device as claimed in claim 1, wherein the tube ofmetallic foil comprises a spiral wrap, wherein one portion of the foiloverlaps another portion.
 6. A device as claimed in claim 1, wherein themetallic foil is resiliently conformable.
 7. A device as claimed inclaim 1, wherein at least part of the metallic coil and at least part ofthe metallic foil are contained within an electrical insulating sleeve.8. A device as claimed in claim 7, wherein at least part of the sleeveis dimensionally heat-recoverable.
 9. A device as claimed in claim 7,wherein a solder preform is located inside the sleeve.
 10. A device asclaimed in claim 8, wherein the sleeve contains a quantity of fusiblepolymeric material located beyond one end of the metallic coil.
 11. Adevice as claimed in claim 1, which further comprises at least one innerelectrical connector that is electrically insulated from the conductiveouter body, for terminating the or each inner conductor of the screenedcable.
 12. A device as claimed in claim 11, wherein the or each innerelectrical connector contains at least one solder insert.
 13. A deviceas claimed in claim 12, wherein the or each inner electrical connectorcontains resiliently deformable means for accommodating a range of sizesof inner conductor(s).
 14. A device as claimed in claim 13, wherein theresiliently deformable means comprises a metallic coil.
 15. A cablehaving a screen and at least one inner conductor, which is terminated atat least one of its ends by means of a device as claimed in claim
 1. 16.A method of terminating a cable having a screen and at least one innerconductor by means of a device as claimed in claim 1, whichcomprises:(i) inserting an exposed length of the cable screen into thetube of metallic foil; and (ii) screwing the metallic coil further intothe outer body until the metallic foil has tightened about the exposedlength of the cable screen.